Question 6: A Perl solution 

sub solve {
    local($_) = @_;
    s{\A\s+}{};
    s{\s+\z}{};

    my $cell_ref = '\b[A-Z][0-9]{1,3}\b';
    if(m{\A($cell_ref)\s*[+]\s*($cell_ref)\z}) {
        return cell_value($1) + cell_value($2);
    }
    else {
        die "Don't know how to solve: '$_'\n";
    }

}